I would keep the 7870. More times than not it is faster than the GTX 660. Physx is pretty pointless IMO and all next gen consoles are running AMD APUs so driver optimization should be pretty good as well.

i got one in early 2009 along with a AMD 4850. killed my card and i didnt know it was the psu that caused the problem. after that i got mad and stopped gaming on this pc untill 2011 when deus ex was coming out, i bought a 460gtx(which i still own) to play it on my pc. it gave me the same problem and i did not know it was the PSU until i asked another forum and they said the PSU is complete crap.

a week later it killed an entire motherboard but i got a refund luckily.